Zigzag Path Research Articles

Vibration fatigue behavior and failure mechanism of Ni-based single-crystal film cooling hole structure under high temperature

Film cooling hole structures significantly influence vibration fatigue performance of Ni-based single crystal turbine blades. This study investigates the vibration fatigue behavior and failure mechanism of film cooling hole structure of Ni-based single crystal superalloy at high temperature by using the plate specimens with film cooling holes. The vibration fatigue cracks are all initiated at the edge of the film cooling hole on specimen surface, and the macroscopic crack path is a straight line path. At the microscopic scale, the crack path at 850 °C is a Zigzag path, but the crack path at 980 °C still shows a straight line path. The crack initiation of the specimen shows the oxidation crack nucleation in the stress concentration area under the coupling effect of high temperature and alternating stress. The macroscopic crack propagation direction at high temperature depends on the stress gradient direction of the resolved shear stress. At the microscopic scale, the crack propagation at 850 °C is the dislocation slip-climb mechanism, and the crack propagation at 980 °C more inclined to produce only the dislocation climb mechanism. The vibration fatigue cracks have the temperature dependence. The high temperature environment promotes the activation of slip system and the enhancement of dislocation mobility, the microscopic raft structure promotes the crack propagation along the γ phase with a large number of dislocations, the oxidation crack promotes the oxygen to enter the alloy matrix, which accelerates the Mode-I crack propagation.

Innozag amplifier: optimizing the Innoslab platform to improve beam quality and gain

This study presents an innovative zigzag-type Innoslab amplifier platform, termed ‘Innozag,’ that merges the essential attributes of both Innoslab and zigzag slab amplifiers. A thorough theoretical and experimental examination has been performed to analyze and compare the gain and amplified beam wavefront distortion of the Innoslab and Innozag amplifiers. Our investigation includes detailed optical path difference computation coupled with examination of the far-field amplified beam profile. The results confirm that the Innozag amplifier reduces the thermally induced wave distortion by up to 40%. Geometric features, particularly the overlapping zones in the zigzag path, increase the gain of the Innozag amplifier. The Innozag design achieves an amplification factor 1.4 times greater than that of the Innoslab amplifier in a five-pass structure.

Zigzag path connects two Monte Carlo samplers: Hamiltonian counterpart to a piecewise deterministic Markov process

Zigzag and other piecewise deterministic Markov process samplers have attracted significant interest for their non-reversibility and other appealing properties for Bayesian posterior computation. Hamiltonian Monte Carlo is another state-of-the-art sampler, exploiting fictitious momentum to guide Markov chains through complex target distributions. We establish an important connection between the zigzag sampler and a variant of Hamiltonian Monte Carlo based on Laplace-distributed momentum. The position and velocity component of the corresponding Hamiltonian dynamics travels along a zigzag path paralleling the Markovian zigzag process; however, the dynamics is non-Markovian in this position-velocity space as the momentum component encodes non-immediate pasts. This information is partially lost during a momentum refreshment step, in which we preserve its direction but re-sample magnitude. In the limit of increasingly frequent momentum refreshments, we prove that Hamiltonian zigzag converges strongly to its Markovian counterpart. This theoretical insight suggests that, when retaining full momentum information, Hamiltonian zigzag can better explore target distributions with highly correlated parameters by suppressing the diffusive behavior of Markovian zigzag. We corroborate this intuition by comparing performance of the two zigzag cousins on high-dimensional truncated multivariate Gaussians, including a 11,235-dimensional target arising from a Bayesian phylogenetic multivariate probit modeling of hiv virus data.

Path planning in additive manufacturing with multi-robot collaboration based on structural primitive partitioning

Directed Energy Deposition (DED) technology is increasingly favored for swiftly fabricating large structural components due to its high printing efficiency. Despite its advantages, challenges persist in achieving satisfactory surface finish and forming precision, hindering its widespread adoption across industries. To address these issues, this paper presents a novel multi-robot collaborative path planning method based on structural primitive partitioning. This method simplifies path planning complexities and seamlessly integrates into process planning software, thereby enhancing overall functionality. This method decomposes complex polygons into tiny primitives (TP), organizing them into TP sets based on bridge and adjacency relations. These sets are then structured into first-level structural TP (F-TP) and second-level structural TP (S-TP), followed by the establishment of monotonic structural TP (M-TP). A minimum rectangular box recalculates the filling path for each M-TP, while the external contour path and internal zigzag path form a complete printing path. Additionally, an optimal printing sequence planning algorithm for multi-robot using a KD-tree-based search algorithm is presented, ensuring the shortest non-productive path and collision avoidance during printing. Experimental verification with four structures of varying geometric features demonstrates a partitioning accuracy of 99.5 % and absence of surface defects in the printed parts. The proposed method presents a viable and effective solution for enhancing the quality of parts produced via DED.

Frequency-selective valley-edge transmission and channeling in phononic-crystal plates with dual topological modulations

In this numerical study, we propose dual-modulated topological pillared phononic crystal (PnC) plates and demonstrate their application in achieving frequency-selective waveguiding of Lamb-wave valley-edge states. We show that both the radius and the height of the pillars in the honeycomb unit cell can be varied, allowing a generalized parameter space to obtain the complete topological bandgaps and two groups of distinct valley Hall phases for designing topological waveguides operating in different frequency ranges. Accordingly, we construct different types of phase domain walls to support valley-edge states using the dual-modulated PnC plates with a lattice constant of 2000 μm and with topological bandgaps opened around the Dirac cone frequency of 426 kHz. The numerical results show that the valley-edge states emerge to cover different frequency ranges and exhibit robust backscattering immunity when propagating along zigzag paths with sharp corners. Furthermore, the transport path of the valley-edge states can be designed to be highly dependent on the operating frequency in different domain walls. Consequently, we design a straight waveguide and three multichannel waveguides to demonstrate frequency-dependent switchable transmission and selective channeling of valley-edge states, respectively. The results of this study pave the way for the development and optimization of topological acoustic circuits using the generalized parameter space approaches and are expected to find promising applications in frequency-controlled and signal-division devices.

Air bubbles crossing a stratified water-diesel fuel interface

This study examines the behavior of a single air bubble moving through a stratified interface between two liquid phases: purified water as the denser liquid and diesel fuel as the lighter counterpart. The study investigates the impact of the upper liquid's height on bubble behavior, particularly under low gas flow rates, using high-speed video imaging. The experimental findings unveil two distinct scenarios: stable and unstable regimes. In stable conditions, the bubble follows a linear trajectory, simultaneously transferring some of the denser liquid into the lighter phase. Conversely, under unstable conditions, the bubble undergoes oscillations, navigating a zigzag or spiral path. The study also explores the correlation between the upper liquid height and the deformation and division of the dragged volume. This comprehensive investigation sheds light on the intricate interplay between liquid heights and bubble dynamics at liquid-liquid interfaces.

Investigation of the influence of defect volume on weld strength during FSW: A simulation and experimental study

Internal defects such as voids/cavities significantly hamper the weld quality, resulting in lower weld efficiency and mechanical properties. Therefore, there is a scope for developing a relationship between quantum of defects and weld efficiency. This research uses a thermomechanical model based on coupled Eulerian-Lagrangian (CEL) to predict defect formation during friction stir welding (FSW) of a 3 mm thick AA2024. A square pin tool is used in current research. A novel concept of defect volume is developed using the Eulerian volume fraction within the weld domain, and a mathematical equation is developed to calculate weld efficiency as a function of defect volume, stir zone temperature, and axial force. The developed model predicted weld efficiency with less than 5 % error with R-squared coefficients of 0.9. The model established effective material flow behavior having an intercalated zig-zag path, resulting in defect-free weld with 86 % weld efficiency at 1500 rpm and 150 mm/min. It has a defect volume of 0.45 mm3. EBSD analysis shows an average grain size of 4.9 and 6.1 µm for defect-free and defective welds, respectively. Material flow, mechanical, and metallurgical characterization of lowest and highest weld efficiency is carried out to understand the underlying weld failure mechanism.

Zig-zag deformations of toric quiver gauge theories. Part I. Reflexive polytopes

We study one-parameter families of U(1)2 preserving deformations relating pairs of toric quiver gauge theories on D-branes probing local toric (pseudo) del Pezzo surfaces. The superpotential deformations are defined by zig-zag paths in the brane tiling and are non-trivial in the chiral ring if the geometry has a non-isolated singularity. In the dual (p, q) web, the deformation is realized as a Hanany-Witten move that reverses a semi-infinite fivebrane. We use these deformations to find RG flows between 4d N\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{N} $$\\end{document} = 1 SCFTs on D3-branes probing local toric (pseudo) del Pezzo surfaces of the same degree, and briefly comment on the interpretation for BPS quivers of rank one 5d SCFTs on S1.

Nusselt number analysis of printed circuit heat exchangers with straight and zigzag channels

Printed Circuit Heat Exchangers (PCHEs) are applied in processes involving high temperatures and working pressures, such as the supercritical CO2 Brayton cycle. These devices are typically designed with semi-circular channels and zigzag paths to enhance thermal performance. In recent years, several Nusselt number correlations for zigzag channels have been proposed to estimate the thermal performance. However, under similar operating conditions and zigzag angles, these correlations yield divergent results for supercritical and non-supercritical condition. No study has compared these correlations to identify the most accurate one. Therefore, this research performed a thermal analysis of PCHEs operating with straight and zigzag channels, using fluids in normal and supercritical conditions. Additionally, it was evaluated existing Nusselt number correlations to determine which ones presents the best result. This study examined 37 Nusselt number correlations, analyzed four experimental studies available in the literature and evaluated a total of 374 experimental data. For straight channels, the error ranged from 3% to 27%, whereas for zigzag channels, the error varied between 3% and 84%. This demonstrates how correlations developed for the same application can lead to discrepant results.

Tuning chemical short-range order for simultaneous strength and toughness enhancement in NiCoCr medium-entropy alloys

The pursuit of enhancing strength and toughness remains a critical endeavor in the field of structural materials. This study explores two distinct strategies to overcome the traditional strength-toughness trade-off. Specifically, we manipulate the chemical composition and short-range order (SRO) of the NiCoCr medium-entropy alloy, which has shown remarkable fracture toughness in recent experiments. Utilizing molecular dynamics simulations, we uncover nano-scale deformation mechanisms during crack propagation. Our findings highlight that optimizing the SRO degree leads to improvements in both atomic scale strength and toughness defined as the area underneath stress-strain curves from MD simulations. In contrast, a trade-off between strength and toughness persists when only manipulating the Ni content in the NiCoCr alloy. Based on the simulation results, we establish a strong correlation between toughness, strength, surface energies, and unstable stacking fault energies. These factors are influenced by the chemical composition and SROs in NiCoCr, with SROs acting as strong obstacles to dislocations, thereby contributing to additional strength. The exceptional toughness of NiCoCr with SRO arises from a synergy of intrinsic and extrinsic mechanisms, including dislocation glide, nanobridging during nanovoid coalescence and zigzag crack path. It is found that, in the presence of SRO, intrinsic toughening mechanisms usually associated with crack tip blunting and dissipation can also facilitate the onset of extrinsic toughening mechanisms of nanobridging and zig-zag crack path associated with nanovoid formation and coalescence. This study emphasizes the importance of tailoring SRO in designing materials with enhanced strength and toughness.

Mechanics of crack initiation, propagation and crack grain boundary interaction in bicrystal silicon using near-tip localized stress calculation

Crack propagation and arrest are important phenomena in polycrystalline silicon. This phenomenon considerably affects the effectiveness of solar cells made up of polycrystalline silicon. To understand the crack propagation in polycrystalline silicon, it is essential to study the bicrystal first. Earlier, crack propagation has been studied in bicrystal materials primarily from the perspective of material behaviour. However, the mechanics part is largely missing. In the present work, crack propagation of bicrystal silicon during uniaxial tension has been studied at the atomistic scale. The silicon bicrystal was formed by joining two single crystals: crystal 1 and crystal 2 of different orientations. Various states like crack initiation, propagation, arrest, re-initiation and crack grain boundary (GB) interaction have been analysed using Stress Intensity Factor (SIF), calculated from the local crack tip virial stress field. Considering the effect of crack tip velocity, the dynamic SIFs at crack propagation state have been converted to the SIF of an equivalent static crack using the generalized expression for anisotropic material. It has been found that for the propagation state, crack propagation continues as long as the equivalent static SIF is greater than the critical SIF (CSIF). In crystal 1, crack propagation is along the low CSIF direction. Therefore, the crack did not change its path and propagated along a straight line. On the other hand, when the crack enters to crystal 2, it follows a zigzag path. Both of these observations have been justified in terms of near-tip calculated SIFs.

Theoretical investigation on graphene induced self-alignment of donor-acceptor structures

Non-covalent functionalization of graphene (Gr) with conducting polymers (CPs) improves the electrical and mechanical properties of both materials owing to the noncovalent π-π stacking interaction between the surface and the aromatic rings in CPs. However, a comprehensive understanding of the self-organization and chain orientation of CPs on the Gr surface remains lacking, which may limit the engineering of CP-Gr complexes with optimized morphology for optoelectronic applications. This study focuses on the Density Functional Theory (DFT) calculations and homemade Python programming code to investigate the self-organization of donor (D)-acceptor (A) type molecules on the Gr surface, aiming to elucidate factors governing the direction of self-alignment. Specifically, basic structural parameters characterizing the aromatic D-A molecules, such as the intramolecular aromatic ring distances, are explored to determine the rules for the preferred alignment direction of the CP monomers on the Gr surface, either in armchair or zigzag paths. Additionally, the influence of Gr on the morphological properties of aromatic molecules, variations in interaction energies between Gr and D-A-D systems with changing A units, and the impact of Gr size on molecular fitting characteristics are examined. The accurate determination of chain alignment direction, which can be applied for all conjugated small molecules and polymers at 2D material interfaces is crucial for guiding experimental studies aimed at tailoring structures and enhanced properties, such as promoting the crystalline domains with high electrical conductivity.

DeepMeshCity: A Deep Learning Model for Urban Grid Prediction

Urban grid prediction can be applied to many classic spatial-temporal prediction tasks such as air quality prediction, crowd density prediction, and traffic flow prediction, which is of great importance to smart city building. In light of its practical values, many methods have been developed for it and have achieved promising results. Despite their successes, two main challenges remain open: a) how to well capture the global dependencies and b) how to effectively model the multi-scale spatial-temporal correlations? To address these two challenges, we propose a novel method— DeepMeshCity , with a carefully-designed Self-Attention Citywide Grid Learner ( SA-CGL ) block comprising of a self-attention unit and a Citywide Grid Learner ( CGL ) unit. The self-attention block aims to capture the global spatial dependencies, and the CGL unit is responsible for learning the spatial-temporal correlations. In particular, a multi-scale memory unit is proposed to traverse all stacked SA-CGL blocks along a zigzag path to capture the multi-scale spatial-temporal correlations. In addition, we propose to initialize the single-scale memory units and the multi-scale memory units by using the corresponding ones in the previous fragment stack, so as to speed up the model training. We evaluate the performance of our proposed model by comparing with several state-of-the-art methods on four real-world datasets for two urban grid prediction applications. The experimental results verify the superiority of DeepMeshCity over the existing ones. The code is available at https://github.com/ILoveStudying/DeepMeshCity.

Multiple chromosomes particle swarm optimization-based coverage path planning for complex surfaces spray painting

Coverage path planning for complex three-dimensional surfaces spray painting is one of the challenging problems in robotics. In this article, we propose a multiple chromosomes particle swarm optimization approach to address the coverage path planning problem for complex three-dimensional surfaces spray painting. Firstly, a layered segmentation method, which is composed of three-dimensional hole identification and region partition, is proposed to divide the complex surface into multiple simple regions with little curvature change and no holes. Secondly, a zigzag path is determined in each region by considering the practical aspects for spray painting. Thirdly, by taking short distance, few turns and high coverage rate into account, a multiple chromosomes particle swarm optimization algorithm is presented to connect the zigzag paths of the regions. Experimental tests are carried out on a complex surface, and the results validate the effectiveness of the proposed approach.

A novel 3D topological metamaterial for controllability of polarization-dependent multilayer elastic waves

The achievement of high-quality wave manipulation and energy concentration has always been considered as state-of-the-art technologies, especially for integrated photonics, acoustics, and mechanics. The exploration of the topological phase of matter provides abundant design tools for robust waveguiding that is immune to backscattering at small defects and sharp bends. Recent research has extended the elastic wave manipulation from 2D edge waveguiding to 3D planar waveguiding. However, most of them are limited to single-mode and single-frequency wave propagation along the designed plane. This paper introduces a novel 3D topological metamaterial structure whose geometrical parameters are specifically configured to obtain dual-mode topological states at distinct frequencies. Parametric studies are presented to demonstrate the controllability of bandgaps and to provide a design principle for preventing the effects of unwanted modes. Topological interface modes with either high group velocity or near-zero group velocity along the z direction are found. Full-scale finite element simulations are presented to uncover the elastic wave propagation behavior. The interesting layer-locked and layer-unlocked waveguiding based on excitation polarization and frequency for both straight path and zig-zag path are demonstrated. The outcomes of this work suggest abundant potential applications related to elastic wave control such as wave filters, energy harvesters, mechanical computers, and the like. This work may also help inspire future research on more complex and sophisticated multi-mode waveguiding in 3D spaces.

Numerical Modeling and Analysis of Transient and Three-Dimensional Heat Transfer in 3D Printing via Fused-Deposition Modeling (FDM)

Fused-Deposition Modeling (FDM) is a commonly used 3D printing method for rapid prototyping and the fabrication of plastic components. The history of temperature variation during the FDM process plays a crucial role in the degree of bonding between layers. This study presents research on the thermal analysis of the 3D printing process using a developed simulation code. The code employs numerical discretization methods with an implicit scheme and an effective heat transfer coefficient for cooling. The computational model is validated by comparing the results with analytical solutions, demonstrating an agreement of more than 99%. The code is then utilized to perform thermal analyses for the 3D printing process. Interlayer and intralayer reheating effects, sensitivity to printing parameters, and realistic printing patterns are investigated. It is shown that concentric and zigzag paths yield similar peaks at different time intervals. Nodal temperatures can fall below the glass transition temperature (Tg) during the printing process, especially at the outer nodes of the domain and under conditions where the cooling period is longer and the printed volume per unit time is smaller. The article suggests future work to calculate welding time at different conditions and locations for the estimation of the degree of bonding.

High-pressure automatic vacuum cleaner using Arduino

In the modern world, household work has been transformed by new technologies. Some machines were designed to automate tasks previously performed by servants, while others employ new energy sources such as electricity and gas to make dwellings cleaner, safer, and more efficient. This paper proposes a high-pressure automatic vacuum cleaner using Arduino to dry-clean an area automatically. The robot covers the entire room or area by using the border analysis technique. The robot travels in a zigzag path and covers the entire area. It analyses the obstacle in the room by using an ultrasonic sensor. The high-pressure pump will suck the dust particles while traveling, thus cleaning the entire room.

COMPUTATIONAL SIMULATION OF SEDIMENT MOTION STABILITY PROCESS ON BRIDGE ABUTMENT DUE TO CRIB PLACEMENT (CASE STUDY: HARAPAN RIVER, JAYAPURA REGENCY)

Erosion occurs when the flow of velocity in a channel exceeds the threshold velocity that causes the bed material to move. This phenomenon is observed in the Harapan River, resulting in significant impacts, such as riverbed lowering and narrowing due to the presence of water structures (bridge abutments) spanning across the river. The objective of this study is to investigate the sediment motion stability around bridge abutments before and after the installation of cribs in order to prevent structural failures. Sediment sampling was conducted at six points around the bridge abutments, using the Pebble Count method along zigzag paths. The grain size of the bed material was classified according to the Sturgess classification standard, and the material dispersion process was analysed using the Hjustorm curve. Design rainfall was transformed into design flood discharge, which was then simulated using the Two-Dimensional Hydrodynamic, comparing the river conditions before and after crib installation. In abutments without cribs, erosion occurred in direct contact with the abutment on the right side for each sediment grain diameter. However, in abutments with cribs, erosion still occurred, but it did not directly contact either abutment despite the presence of a crib. The crib prevented and protected the abutments from being eroded by the riverbed.

Near-infrared self-assembled laser based on Ag<sub>2</sub>Se quantum dots

The development of colloidal near-infrared quantum dots (QD) lasers has been hindered by the high state degeneracy of lead salt QDs and the difficulty in coupling colloidal quantum dots to the resonant cavity. In this study, we show that above challenges can be addressed by the self-assembly laser based on Ag<sub>2</sub>Se QDs. Ag<sub>2</sub>Se QDs with the lowest quantized states 2-fold degeneracy are used to replace lead salt quantum dots to achieve low threshold near-infrared optical gain. We employ the finite element method to deeply analyze the mode field distribution and oscillation mechanism of the coffee-ring microcavity. Our results reveal that the light field oscillates in a zig-zag path along the cross-sectional area, indicating strong coupling between the QDs and the cavity mode. Furthermore, we investigate the relationship between cavity length and free spectrum range and laser emission wavelength. Leveraging this relationship and the gain spectrum characteristics of Ag<sub>2</sub>Se QDs, we design a single-mode near-infrared laser and conduct a comprehensive analysis. Using simulation results to fabricate a single-mode near-infrared Ag<sub>2</sub>Se QD coffee-ring microlaser, which exhibits a linewidth of 0.3 nm and a threshold of 158 μJ cm<sup>-2</sup>. Currently, it holds the record for the lowest laser threshold among near-infrared colloidal QD lasers. Increasing the laser cavity length, resulting in an increase in the emission wavelength from 1300 nm to 1323 nm. In addition, the toxicity of Ag<sub>2</sub>Se QDs is remarkably negligible. Our work promotes the development of environment-friendly near-infrared lasers to practical lasers.

Effects of path patterns on residual stresses and deformations of directed energy deposition-arc built blocks

ABSTRACT Deposition path patterns play an important role in controlling residual stresses and deformation in direct energy deposition-arc (DED-arc) process. In this paper, the effects of various path patterns on the evolution of the temperature history, residual stress distribution, and substrate deformations are investigated through experiments and finite element analysis. The predicted results of temperature fields and substrate deformations are verified experimentally by the infrared thermal imager and the laser profile scanner, respectively. It is found that the path patterns have significant effects on the stress distribution in the first few layers, and the minimum substrate deformation is obtained by the zigzag path along the short edge of the block. The proposed finite element method and measuring method are confirmed to be effective and feasible, providing valuable insight into the residual stresses and deformations control in the DED-arc process.